Yamaha A4000: Encoder Fix + Adding a Compact Flash Drive

Update from 2016: It's been a few years since I've made these modifications. I'm sorry to say the encoder fix is not a complete long term solution. I'm beginning to have problems with skipping in the encoders. The fix might buy you a little more time, but in the end replacement encoders are likely the only real solution.

I recently acquired a Yamaha A4000 rack sampler, little brother of the Yamaha A5000. The synthesis structure is deep and it sounds great. However, this machine is from the late 90s and therefore has a few annoying quirks. First and foremost, the encoders are very finicky due to age and a design flaw. Secondly, the machine uses SCSI for storage and the required equipment is very impractical. Finally, with a SCSI hard drive and the case fan, this machine runs very loud. I wanted to fix all these issues.

I should say do these modifications at your own risk. These are not simple modifications and I accept no responsibility for any damage that may be caused. That said, here are the steps I took.

Encoder Fix

The most important problem was the encoder issue. The machine uses sealed encoders with a click switch which start to act erratically after a few years. Since the encoders are sealed, they are very difficult to clean. I tried the DeOXIT route, using the tiny gap between the push switch to get the chemical inside the encoder. This resulted in a very slight improvement, but did not fix the underlying issue.

After doing some research, I discovered that the settle time for the bouncing contacts inside the encoder is very low and can result in incorrect readings due to the software routines used by Yamaha. The solution is to slow down the bouncing signals coming from each encoder. A few others have made simple lag processors out of 1uf capacitors to achieve this result. Later it was discovered that adding a 470 ohm resistor in series with each capacitor will protect the encoder contact from excessive voltage. This modification will also electrically clean the contact each time it turns.

To begin, I dismantled the unit. Many black screws hold the top of the case on; remove the proper screws on the back, top, and bottom to remove the cover. The hard drive brackets must be removed to access the encoder board. The red arrow indicates where the brackets connect. Two screws on top of the encoder board must be removed and the indicated cables must be removed.

The encoder board is also held on by hex nuts and washers on the front. To access this point, remove the faceplate by removing the three screwes on the bottom. Remove the hex nuts and washers and the board should slide loose. Do not remove the metal bracket above, it is not necessary to access the board. Be sure to save each screw and hex nut in a secure place for when everything is reassembled.

Here is the solder side of the encoder board. The blue arrows indicate the pins of interest on an encoder. This is where the capacitors and resistors will be attached. Some people choose to attach the circuit directly to the board; I worried about short circuits with the case so decided to place the circuit on a separate board. The gray arrow indicates a common ground to use for the circuit.

Here is the modified board with the additional circuit. I used electrical tape over the connections for added strength and protection from short circuits. Originally I tried to use the edge connector for all the points, but the connections were just too close together. Be sure to use a common ground to save on the amount of wires that must be routed. Also be sure to leave enough slack to mount the board elsewhere in the unit. I used 24-gauge wire for the connections to the board.

Here is a diagram of the circuit. I used 50V capacitors as I had many extra, but lower ratings may also be acceptable. Everything was mounted on a simple perfboard from Radioshack. Run the wires from behind the encoders as the encoders are flush with the faceplate.

It was difficult to find a place to mount the board. I originally thought I could fit everything above the encoder board, but I would have to make a very skinny long board to do so. There is a hard drive bracket that was used to hold SCSI drive. This serves as a very convenient place to mount additional items if there is no drive present. I had to add additional mounting holes to fit the perfboard. Insulted standoffs were used to avoid short circuits.

SCSI-to-Compact Flash Drive Replacement

Also visible in this photo is the SCSI-to-Compact Flash drive replacement. I used the same bracket to mount the additional equipment, again on insulted standoffs. Electrical tape was used on the top power connector to avoid short circuits.

The SCSI-to-IDE bridge is increasingly hard to find. Prices used to hover around $35 dollars a few years ago, but have shot up to over $100 in the last year. I guess these things are no longer being produced, get one while you can. Ebay is a good source for this part. I believe you need to set the terminator on the bridge to active, I can't remember.

Get the simplest IDE-to-Compact Flash drive possible, no dual card abilities. It is best if it can plug directly into the SCSI-to-IDE bridge. The two items will hold together very well just using friction. I mount everything using the screw holes on the IDE-to-Compact Flash drive.

The Compact Flash card should be fast to avoid timing errors as many conversions are taking place. The A4000 only supports 8GB of storage, separated into 1GB partitions. Anything larger will not be used. Be sure to get a name brand card as there are many, many counterfeit junk compact flash cards out there.

The remaining items are used for wiring everything together. The power connections for each unit are surprisingly tricky and many require additional converters and splitters. Use zip ties to keep everything tidy. Use the hard drive bracket for mounting as that is what is being replaced and it is easy to remove to add additional mounting holes.

There is no way around how slow SCSI access is on the A4000. For a slight (and I do mean slight) improvement, use an IDE drive instead and put up with the noise. You will need to format the drive into 8 partitions before it can be used. Also note, it takes much longer for the unit to start up when using drives. Expect to wait a 90 seconds or more for everything to be ready to use. I was unaware of this fact and thought things were broken.

Finally, if you remove the hard drive, you can disable the case fan by unplugging the two wire connector leading out of the power supply. The power supply was designed to cope with the heat of a SCSI hard drive for hours at a time. Since this source of heat has been removed, the fan can be disabled.

After these modifications, I have a totally silent A4000 with lots of storage and smooth encoders. The encoder modification is like night and day, the machine is now a joy to use and very quick to get around.